1. Field of Invention
This invention relates to holographic films, both metallized and non-metallized, employing cycloolefin copolymers (COC), and in particular to unique multilayer holographic films that include a holographic image in the COC layer, in the form of a micro-embossed image.
2. Background Art
Holographic films, both metallized and non-metallized, are known in the art, and are utilized for a wide variety of applications, e.g., in flexible packaging as substrates for food products, as gift wrapping paper and as a decorative component in non-flexible packages or rigid packages, e.g., packages for tubes of toothpaste, cereal boxes, detergent boxes, etc. For some applications, and in particular in the packaging of food products, it is desirable that these holographic films have good oxygen and water vapor barrier properties. Although some non-metallized holographic films may have reasonably good oxygen and water vapor barrier properties, the primary function of the micro-embossed holographic image is to impart a decorative appearance to the film. Providing a metallized layer on the micro-embossed holographic image enhances image quality (e.g., brilliance) and also the oxygen and water vapor barrier properties of the holographic films.
Prior art multilayer holographic films have been made both by coextrusion and coating processes.
Prior art coextruded films have employed semi-crystalline copolymers to form the outer layer for receiving a micro-embossed holographic image therein. Specifically these semi-crystalline outer layers have included Ziegler-Natta catalyzed propylene-ethylene copolymer (3-7% ethylene) layers or propylene-butene copolymer layers. A coextruded holographic film including a propylene-butene hologram receiving layer, which was invented by Andrew F. Wilkie, the inventor herein, and is covered in U.S. Pat. No. 6,677,029, has a higher gloss and more brilliant holographic image than the holographic films including the above-identified Ziegler-Natta catalyzed propylene-ethylene copolymer.
Although the use of a hologram-receiving layer including a butene-propylene random copolymer provides improved gloss and a more brilliant holographic image than the prior art holographic films employing a propylene-ethylene copolymer layer for receiving the holographic image therein, there is a continuing need for improved holographic films having even better gloss and brilliance.
Prior art holographic films manufactured by a coating process include films having an acrylic (amorphous) hologram-receiving layer provided on a polypropylene or polyester core. These acrylic coatings generally are applied off-line after fabrication of the base film. Interestingly, although the unembossed acrylic coating has a gloss that is higher than the prior art, unembossed propylene-butene copolymer layer, after embossing the coated film is no more brilliant than the film including the embossed, propylene-butene copolymer layer. Thus, it is not predictable that starting with a higher gloss, unembossed film will necessarily result in a corresponding increase in the brilliance of the film after the film has been micro-embossed to provide a holographic image therein.
Although an outer layer formed of 100% Ziegler-Natta catalyzed or metallocene catalyzed isotactic polypropylene homopolymer has the desired gloss (e.g., on the order of 135 or higher gloss units as measured at a 20° angle employing ASTM D2457-97) these polymers have an embossing temperature that is too high to permit their effective use in the holographic films of this invention.
Cyclic-olefin copolymers (sometimes referred to as “COC”), which are employed in the unique and unobvious holographic films of this invention, have been known since approximately 1954 (DuPont, U.S. Pat. No. 2,721,189). These cyclic-olefin copolymers have been employed to make amorphous, plastic based products. In particular, due to the clarity of the COC plastics, they typically have been used in lenses for cameras, copiers, CD players, prefillable syringes and small vials produced by an injection molding operation followed by stretch blow molding.
It also has been suggested to form biaxially oriented films of COC for use as food wrapping, such as twist wrappers for candy.
It also has been recognized that films formed from COC can be metallized for use in electrical applications, such as for capacitor films.
Although COC has been available for use in making plastic films for several years, there has been absolutely no recognition that COC can be employed as a plastic layer in a multilayer holographic film, wherein the COC layer is required to receive and retain a micro-embossed image therein. Nor has there been any recognition of metallizing a COC micro-embossed layer to enhance the brilliance, or clarity of the micro-embossed image and improve the oxygen and water vapor barrier properties of such film. Stating this another way, there has been absolutely no recognition in the prior art that COC can be employed to form a hologram-receiving layer that has the capability of both receiving and retaining a micro-embossed image therein, and thereafter, if desired being metallizable to enhance the brilliance of the micro-embossed image and improve the oxygen and water vapor barrier properties of the film.
Disclosures of employing COC in a number of different products are included in the following publications:                1. Offprint of Plastic Special 6/1999 titled “Extruding COC without Fish Eyes”        2. U.S. Patent Publication No. 2005/0170124, disclosing a glossy film including a cycloolefin copolymer as a filler in a polyolefin-based resin film.        3. U.S. Patent Publication No. 2004/0018355, disclosing a forgery-preventing film, which preferably is a multilayer structure. Although ethylene-cycloolefin copolymers are generally disclosed as one of numerous types of copolymers that can be used in a first layer of the film, the most preferred polymers are identified as propylene-based resin and high-density polyethylene. Moreover, the only specifically enumerated use for the ethylene-cycloolefin copolymers in the holographic layer is as an organic filler for a thermoplastic polyolefin resin layer, similar to the disclosed use in the above identified '124 patent publication.        4. Other publications of background interest are: U.S. Pat. No. 6,830,713; U.S. Pat. No. 6,852,407; U.S. Patent Publication No. 2006/0013984; U.S. Patent Publication No. 2005/0078366; U.S. Pat. No. 6,808,658; U.S. Pat. No. 6,827,886; Pure Appli. Chem., Vol. 77, No. 5, pp. 801-814, 2005, “Chemical Structure and Physical Properties of Cyclic Olefin Copolymers (IUPAC Technical Report), prepared by Ju Young Shin, Ji Wong Park, Chenyang Liu, Jiasong He and Sung Chul Kim; and Topaz Advanced Polymers Technical Publication for Cyclic Olefin Copolymer (COC).        
All of the patents and other publications identified herein are incorporated herein by reference in their entireties.